The invention relates to an X-ray diffraction apparatus for examining a specimen.
A known apparatus of this kind comprises first and second diaphragm tubes in coaxial alignment, which are axially displaceable with respect to each other and define a circular diaphragm slit with an adjustable width between them, a cylindrical film cassette enclosing the diaphragm slit and provided with an axial slot for admitting the X-rays, a collimator for the X-rays arranged outside the film cassette opposite to the cassette slot and the diaphragm slit, a specimen spindle enclosed by the first diaphragm tube on which the specimen to be examined may be mounted opposite to the diaphragm slit, adapted to perform an oscillating or continuous rotation, and an elongated carrier on which supports for each of the diaphragm tubes are arranged near its ends.
Instruments of this kind are frequently used for the examination of crystals, but may also be used for powder radiographs.
In the known instruments of the above-mentioned kind, the diaphragm tubes are completely or substantially completely enclosed by the associated supports. Where an integral film cassette is used, it is consequently impossible to remove the film cassette from the instrument without dismounting one of the diaphragm tubes, in some cases together with the associated support. This is a disadvantage in cases in which a new film must be inserted during a measurement. This disadvantage is aggravated if the examination of the specimen must occur at a prescribed temperature. In such cases, it is usual to keep the specimen at the required temperature by a heat exchange with a cold or hot gas stream, which must be introduced through the second diaphragm tube, since this is the only way through which the specimen is attainable. The gas stream is supplied through a conduit terminating shortly before the specimen and secured to the inside of the second diaphragm tube. As a consequence a removal of the film cassette is only possible by dismounting not only the second diaphragm tube, but also the supply conduit for the gas stream. This is, of course, very laborious, but it also leads to a considerable change of the temperature of the specimen, which causes a discontinuity in the measurement. Examinations in which the temperature of the specimen is not allowed to surpass a certain limit, for instance the melting point, may even be rendered impossible.
It has been proposed to remove the above-mentioned difficulties by the use of a film cassette consisting of two semi-cylinders which are joined when the cassette is inserted in the apparatus. However, the shape of such a cassette is not sufficiently stable, so that the position of the image on the film is not accurately determined. In addition, the position of the image must be measured afterwards on two separate film halves, which leads to a further inaccuracy.